Has a merury II set up and got strong signal, but when connect both LNB to Diseqc switch loose signal.

There is a duall LNB work great when connect to one sat AMC KU. When connect both LNB no signal or picture What am I doing wrong?

What make and model of lnb. If it is a dual, you should not need to connect both ports to one reciever. Do you have more that one dish?